The invention relates to a preprocessing method for a motion estimator utilized in he processing of television image sequences.
Motion estimation is becoming ever more important in systems such as standards converters, high-frequency converters better known as xe2x80x9cup-convertersxe2x80x9d, de-interlacers or coders, while the algorithms are becoming more powerful and more easily integrated.
There are various types of motion estimator, for example the block-matching type, the point-to-point or xe2x80x9crecursive-pelxe2x80x9d type. In order to improve the operation of these motion estimators and raise their performance, the images transmitted to them are generally preprocessed. This may, for example, be a subsampling followed by a filtering so as to reduce the size of the image in order to simplify the circuits and increase the processing speed, a low-pass filtering to remove some of the high frequencies so as to facilitate the operation of the motion estimator, a line interpolation for each frame so as to obtain new frames whose lines correspond (this is in fact a de-interlacing), etc. For example the estimator of the recursive-pel type described in French Patent No. 8812468 requires a preprocessing of the images in order to operate satisfactorily. Likewise, the estimators of the xe2x80x9cblock-matchingxe2x80x9d type are often preceded by a preprocessing of the images.
Motion estimators operate imperfectly with regard to interlaced images containing horizontal contours: there is spectral aliasing in these areas, and the successive frames, exhibiting different lines, are not correlated there. Motion estimators such as those of the recursive-pel type then diverge in these areas.
The preprocessing operations described earlier, for example spatial filtering, bring about an overall improvement in the performance of the estimators but do not satisfactorily resolve the defects of motion estimation which may be particularly visible in the motion-compensated or estimated image and give rise to a degradation in the quality of the image.
The aim of the invention is to alleviate the aforementioned drawbacks.
Its subject is a method of preprocessing a video image sequence consisting of a succession of interlaced frames for estimating motion between a first and a second frame, characterized in that a temporal filtering is performed on the basis of at least two input frames so as to deliver each of the two frames utilized by the motion estimator.
Its subject is also a device for implementing the method, characterized in that it comprises:
a memory for storing four successive interlaced frames,
vertical filters for transforming these four stored interlaced frames into four progressive frames,
a temporal filter for delivering two filtered frames, the first on the basis of the progressive frames corresponding to the first three stored frames and the second on the basis of the progressive frames corresponding to the last three stored frames,
the motion estimation being carried out on the basis of these two filtered frames.